“You can’t build a reputation on what you’re going to do”. That quote is from Henry Ford. While Mr. Ford screwed up in relation to the environmental and energy crisis we face today, I think he was spot on with that observation.

Nobody wants to see “under construction” pages
Nobody wants to see “coming soon” pages

There’s little point in having a person click through to a page to see those sorts of messages. Firstly, expectations are built up when they click on a link as to what they are going to see. Then there’s disappointment and frustration when nothing appears except those words and maybe a graphic underlining the point there is nothing to see. You may as well put LOSER! in 36px on the page :)

A “coming soon” page really only has one place - as a home page when you’ve designed a marketing campaign with the sole intention of building up anticipation of an imminent rollout and you’re collecting email addresses for notification.

Other than that, if you have a page or site under construction, remove links to those pages until they are ready for prime time. Under construction pages can also have a negative effect on search engines as they have no content; it can take longer to rank that page once it finally does have content.

“Coming soon” announcements should also be kept to a minimum. “Soon” is a highly subjective term. To me, soon means within a week or so. To some it can mean a day. To merchants, it can mean a year - it’s a hook that too many have used for features that never arrive; and many consumers are wary of this. If you know for sure when a specific feature will be available; give the date. People are more concerned with what you offer now rather than what you will/might offer at an unspecified point in time.

Related:

Beginners guide to building an ecommerce web site